In various medical and sports-related fields, it is important to accurately measure the forces created by, or placed upon, a person or animal during walking, running, or other movement. This analysis is useful during physical therapy to detect problems in need of therapy and to monitor the progress of a patient. This analysis can also be used for measuring the intensity of exercise and effect of the exercise on a patient during physical therapy. Further, such analysis is useful to monitor the stride of an animal, such as a horse, during training of the animal. Force measuring devices have been developed as a tool to provide detailed, objective force measurements to assist in this type of movement analysis.
U.S. Pat. No. 4,195,643 to Pratt, Jr. discloses one example of a force measuring device which uses ceramic capacitors to detect forces applied in a vertical direction against the device. The ceramic capacitors produce an electrical signal representative of the forces applied thereto, and these signals are analyzed to study the motion of the person or animal on the device and gauge the physiological condition of the person or animal on the device. U.S. Pat. No. 5,005,140 to Havriluk discloses another force-measuring device which measures forces applied to fluid-filled tubes or containers by detecting pressure changes within the fluid containers. The fluid containers are, for example, attached to the foot of a person. As the person begins to walk, the pressure fluctuates in various regions of the fluid containers, and these pressure changes are detected by force transducers.
Unfortunately, the prior art force measuring devices are only adapted to measure forces in a single, generally vertical direction. The devices are not adapted to measure both vertical forces and shear forces applied by a person or animal, information which would be highly useful in a movement analysis.